1. Field of the Invention
The present invention relates to a flash device, lens-fitted photo film unit, camera, and producing method for the same. More particularly, the present invention relates to a flash device in which a light amount control circuit can be powered by a simple construction, lens-fitted photo film unit, camera, and producing method for the same.
2. Description Related to the Prior Art
One of simple types of cameras is a lens-fitted photo film unit, which has a housing including a taking lens and a shutter mechanism, and is pre-loaded with unexposed photo film. In order to take an exposure at night or indoors, there is a type of the lens-fitted photo film unit in which an electronic flash device is incorporated.
In the flash device used in the lens-fitted photo film unit of the presently available type, flash light of a predetermined amount is applied to a photographic object irrespective of an object distance. If the object is at a near distance, the object is photographed in an overexposed state. There occurs a problem in that the object is reproduced in a photographic print in too low a density and too bright a state in which the object is visibly indistinct. Also, a background is photographed too darkly even when the object is reproduced properly.
In a compact camera, an automatic flash device is used as the flash device, and can operate for automatically adjusting an amount of light. A flash discharge tube is driven to emit flash light in the automatic flash device. Immediately, a photo receptor element such as a photo transistor receives flash light reflected by the object. The automatic flash device effects calculation of integration of a photoelectric current generated by the photo receptor element upon receiving the flash light. When the integrated amount comes up to a predetermined level, a thyristor as a non-contact switch is turned on to quench discharge of the flash discharge tube. Light emission of the flash discharge tube is discontinued. Therefore, the flash light amount can be controlled appropriately according to the object distance of the object.
When the automatic flash device mentioned above is used, a specialized power source circuit is used in a camera or the like, because it requires voltage of several volts higher than a power source of a dry battery for the purpose of energizing the photo receptor element, the thyristor and the like. However, a combination of a light amount control circuit with the lens-fitted photo film unit has a problem in that no known construction can suitably convert voltage of 1.5 volts to sufficiently high voltage for the light amount control circuit. The specialized power source circuit used in a camera has a considerable size and is expensive, and inconsistent to the features of the lens-fitted photo film unit which should be simple.
In view of the foregoing problems, an object of the present invention is to provide a flash device in which a light amount control circuit can be powered by a simple construction, lens-fitted photo film unit, camera, and producing method for the same.
In order to achieve the above and other objects and advantages of this invention, a flash device has a booster circuit including primary and secondary windings, the secondary winding generating high voltage when power source voltage is applied to the primary winding. A main capacitor is charged by the high voltage in the secondary winding. A flash discharge tube is connected in parallel with the main capacitor, for emitting flash light upon discharge with electric energy from the main capacitor. A trigger circuit discharges the flash discharge tube upon a switching operation. A photo receptor element measures reflected light from an object illuminated by the flash light, to output a light amount signal. A light amount control circuit quenches discharge of the flash discharge tube when an integration value of the light amount signal comes up to a predetermined value. A powering voltage generator circuit is connected with the secondary winding, for generating powering voltage adapted for powering the light amount control circuit in response to operation of the trigger circuit.
The light amount control circuit includes a first capacitor for integration of the light amount signal. A first switching element becomes conductive when voltage across the first capacitor comes up to the predetermined value. A second capacitor is charged by application of the powering voltage, and is discharged upon rendering the first switching element conductive. A second switching element becomes conductive upon discharge of the second capacitor, to quench emission of the flash light from the main capacitor by discharging the main capacitor.
The powering voltage generator circuit includes a driving capacitor for being charged by the high voltage in the secondary winding, and for being discharged through the flash discharge tube in response to operation of the trigger circuit. A Zener diode is connected in series with the driving capacitor, for generating the powering voltage upon discharge of the driving capacitor.
The photo receptor element is a photo transistor, connected in series with the first capacitor, for being supplied with the powering voltage by the powering voltage generator circuit, to generate a current constituting the light amount signal according to the object light amount.
The first switching element is a first thyristor having a first gate, connected in parallel with a series of the photo transistor and the first capacitor, the first gate being connected with a juncture point between the photo transistor and the first capacitor. The second switching element is a second thyristor having a second gate, connected in parallel with the main capacitor, the second gate being connected with the second capacitor.
Furthermore, a choke coil is connected between an anode of the second thyristor and the main capacitor, for protecting the second thyristor by preventing a current from flowing at a high frequency from the main capacitor to the second thyristor.
The flash discharge tube has one end connected between the choke coil and an anode of the second thyristor.
Furthermore, a time adjusting capacitor is connected in series with the first thyristor, for increasing time before rendering the first thyristor conductive.
Furthermore, a front wall is provided. A flash emitter is secured to the front wall, for containing the flash discharge tube, to emit the flash light to the object. A charging operation portion is disposed in the front wall, for being externally actuated, to turn on the booster circuit.
Furthermore, a sync switch has a pair of switch segments for being shifted to a contacted state by a shutter mechanism upon actuation thereof, to switch on the trigger circuit.
In one aspect of the invention, a lens-fitted photo film unit includes a main body pre-loaded with photo film. A booster circuit includes primary and secondary windings, the secondary winding generating high voltage when power source voltage is applied to the primary winding. A main capacitor is charged by the high voltage in the secondary winding. A flash discharge tube is connected in parallel with the main capacitor, for emitting flash light upon discharge with electric energy from the main capacitor. A trigger circuit discharges the flash discharge tube upon a switching operation. A photo receptor element measures reflected light from an object illuminated by the flash light, to output a light amount signal. A light amount control circuit quenches discharge of the flash discharge tube when an integration value of the light amount signal comes up to a predetermined value. A powering voltage generator circuit is connected with the secondary winding, for generating powering voltage adapted for powering the light amount control circuit in response to operation of the trigger circuit.
The photo receptor element is disposed on a front side of the main body. Furthermore, a front cover covers the front side of the main body. A photometric window is formed in the front cover, for passing the reflected light from the object to the photo receptor element.
Furthermore, a flash circuit board has the booster circuit, the main capacitor, the flash discharge tube, the trigger circuit, the photo transistor, the light amount control circuit, and the powering voltage generator circuit. A positioning mechanism positions the flash circuit board between the main body and the front cover.
Furthermore, a battery is contained in the main body, for generating the power source voltage.
In another aspect of the invention a camera is provided instead of the lens-fitted photo film unit.
In a further aspect of the invention, a lens-fitted photo film unit producing method for producing a lens-fitted photo film unit is provided. In the lens-fitted photo film unit producing method, the flash circuit board is secured to the main body. The front cover is secured to the main body in positioning the photometric window at the photo receptor element in the main body, and in positioning the charging operation portion at the flash circuit board in the main body.
Furthermore, a shutter mechanism is secured to the main body, the shutter mechanism including a shutter blade for providing an exposure to the photo film. A sync switch is secured to the main body in a predetermined position relative to the shutter blade in the main body before the front cover is secured to the main body, the sync switch being shifted to a contacted state by a portion of the shutter blade upon actuation of the shutter mechanism, to switch on the trigger circuit.
Furthermore, a photo film cassette is inserted in a cassette loading chamber in the main body. In the step of inserting the photo film cassette, the photo film is inserted into a photo film chamber in the main body in a form wound as the roll after being drawn from the photo film cassette. After the steps of inserting the photo film cassette and the photo film, the rear cover is secured to the main body before the step of securing the front cover, wherein the rear cover closes the cassette loading chamber and the photo film chamber.
In an additional preferred embodiment, a flash device comprising an oscillation transformer, including primary and secondary windings coupled with each other in mutual induction, there occurring an induction current flowing in a secondary winding upon flowing of a current in the primary winding, the induction current adapted for charging a main capacitor. A flash discharge tube is triggered by application of trigger voltage, for emitting flash light by discharging the main capacitor being charged. A light amount control circuit receives the flash light reflected by an object to be photographed, and quenches discharge of the flash discharge tube when an amount of the received reflected flash light comes up to a predetermined level. A driving capacitor is charged by back electromotive force generated in the primary winding, and generates powering voltage adapted for powering the light amount control circuit in emitting the flash light.
In a further preferred embodiment, a flash device includes an oscillation transformer, including primary, secondary and tertiary windings coupled with one other in mutual induction, there occurring an induction current flowing in a secondary winding upon flowing of a current in the primary winding, the induction current adapted for charging a main capacitor. A flash discharge tube is triggered by application of trigger voltage, for emitting flash light by discharging the main capacitor being charged. A light amount control circuit receives the flash light reflected by an object to be photographed, and quenches discharge of the flash discharge tube when an amount of the received reflected flash light comes up to a predetermined level. A driving capacitor is charged by electromotive force of induction generated in the tertiary winding by changes in a current flowing in the secondary winding, and generates powering voltage adapted for powering the light amount control circuit in emitting the flash light.
According to the present invention, the light amount control circuit can be powered by a simple construction, because the high voltage generated by the secondary winding in the flash control circuit can be utilized in a simple construction.